Electric distribution system



May 22, 1945. L. R. BoGARDus I vELECTRIC DISTRIBUTION SYSTEM OriginalFiled July l8, 1959 Pafented May 22, 1945 l ELECTRIC DISTRIBUTION SYSTEMLeonard R. Bogardus, Detroit, Mich., assigner to Packard Motor CarCompany,- Detroit, Mich., a corporation of Michigan Original applicationJuly 18, 1939, Serial No.

285,204. lDivided and this application April 18 l1942, Serial No.439,593

9 Claims.

This invention relates to distribution systems for electricity and moreparticularly to improved bus systems for high current, singlephase,inductive loads such as resistance welding equipment, inductionlfurnaces, and the like.

It is the general object of the present invention to provide anelectrical distribution system capable of delivering greater loads forlonger distances with less voltage drop than with systems heretoforeused for similar purposes and having a comparable amount of metal, thenew system including connected sections of coaxially arranged inner andouter tubular conductors insulated from each other.

An important feature of the novel bus system comprises simple andeffective means for taking taps from the inner tubular conductor wherebywelding equipment may be spaced at any desired intervals along the busand readily adjusted in position at any time in accordance with therequirements of the work being done.

Another important feature of the invention comprises a tap constructionfor association with an inner tubular conductor and including a bolt andsleeve construction adapted to be insertedthrough openings in the wallsof the outer and insulating tubes and clamp onto the wall of the innertube.

Other and further objects and features of the invention, andparticularly details of construcy tion, will be more apparent toy thoseskilled in the art upon a consideration of the accompanying drawing andfollowing specification wherein is`disclosed a single exemplaryembodiment of the invention with the understanding that suchcombinations of parts shown, variations thereof and modifications of theelements may be made as fall within the scope of the appended claimsvwithout departing from the spirit of the invention. Further advantagesof the whole system and a more complete description thereof appear in mycopending application Serial No. 285,204 for Electric distributionsystems, filed in the United States Patent Oflice July 18, 1939, ofwhich application this is a division. This application has matured toPatent No. 2,295,825, grantedrSeptember 15, 1942.

In said drawing:

Figure 1 is a longitudinal central section through, and a partialelevation of a bus system constructed according to the present inventionshowing various types of fittings for connecting the conductor tubes;

Figure 2 is a transverse section on line 2-2 of Figure l showing a tapconstruction;

Figure 3 is a section on line 3--3 of Figure 2;

Figure 4 is a perspective View of a tap part; and

Figure 5 is a fragmentary sectionalview on an enlarged scale of anapproved form of joint between the sections of insulating tube.

The problem of adequately supplying the very large loads to electricresistance Welders, induction furnaces, and othervery heavysingle-phase, low power-factored loads has not. hitherto met with anentirely satisfactory solution because the feeders or busses supplyingthe current must be able to meet unusual requirements. AFor the sake ofsimplicity the problemsv of resistance welding loads will be consideredherein as an adequate example of various types of load to which thepresent invention is applicable. Such welding loads, particularly inproduction plants, such as those fabricating automobile bodies, are verydifferent from the ordinary light and power loads. Their characteristicsof low powerfactor, short time and very high currents, the requirementfor using single-phase, and the desire for excellent regulationnecessitate a different arrangement of conductors than has heretoforebeen used. The use of conventional motor wiring methods has been foundentirely unsuited.

The earliest practice made use of a pair of heavy feeder cables in aconduit, but this soon exhibited marked disadvantages both in electricalcharacteristics and in the difficulty of making taps when welderpositions were to be changed or new ones added. In certain productionwork the weldingequipment is distributed every fewy feet along thebuslines and must be changed in position from time to time as changes inproduction require. The conductors from the busses to the weldingtransformers and from these transformers to the guns must be kept at aminimum length so that new taps are imperative when equipment is to bemoved even a very few feet.

Following this arrangement it became quite universal to use four or morefeeder cables just taped together so that tapping for welder supply wasnot so much of a problem but still relatively diflicult. The use of aplurality of cables resulted in a better interlinkage of magnetic fieldsand thus reduced the inductive reactance to some extent, but still thecombined resistance and reactance drops were such that all welders hadto Abe kept within one or two hundred feet of the main supplytransformer and only a lim- ,rigid, insulating tube.

ited number could be distributed along the feeder system.

Following the wide use of the taped cables came the use of interlacedbus bars. This system makes use of rectangular strips or bars of copperof large cross-section separated by suitable insulation strips. Usuallyfour, eight or more bars were used with adjacent bars on oppositecircuit legs to improve the inductive reactance. The tapping diflilcultywas not materially reduced by this construction and such bus barequipment became exceedingly heavy and cumbersome because portions rofthe bars were exposed and required a conduit or duct system or some formof housing which protected them from chance short circuits and at the:same time permitted access for tapping.

In accordance with the present invention an extremely simplieddistribution system has'been worked out in `which but two conductors`are used, veach large diameter copper tubes, coaxially disposed,closely adjacent to eachl other, and separated by a `thin-walled,preformed, With this 4construction the reactance was immediately reducedto a `point where it is slightly less than the ohmic resistance andcontrary to expectations it was found that -`although using considerablyless .copper than the comparable interlaced bus system, more Welderscould .be used and the distance to which current is conducted to themcould be substantially doubled while at the same time maintaiing betterregulation than had been experienced with .the interlaced bus system.

The 4practical embodiments of the present invention may take many formsand for .the purpose of illustrating the invention there is shown VinFigures 1 Yto 4 inclusive a combination of parts which -has been ,foundextremely satisfactory for supplying current to a production welding jobwhere Welders of various sizes, types, and uses yare very closelyarranged throughout the full length of `a 600 foot coaxial bus.

The bus itself comprises aseamless, drawn copper outer tube 40 ofstandard 4 inch iron-pipe size, and an inner tubular member 4'1 of 3inch extra heavi7 iron-pipe size. This provides a close approximation ofthe cross-sectional area of the outer tube, ythe respective areas incircular mils being 4,040,000 and 3,835,000. The diameter to wallthickness ratio of each of these tubes is greater than 10 and thespacingof the two is as close as possible to keep the inductance low.The provided spacing between the outer surface of the inner tube and theinner surface of the outer tube is less than that essential for airinsulation at the 480 volts used. To mechanically `and electricallyseparate the tubes and support the inner from the outer, a close fittinginsulation tube 42 is provided, preferably of some molded and reinforcedplastic such as the material sold under the trade name Micarta Thesections of conducting and insulating tubing can 'be readily puttogether by sliding or telescoping one `within the other, the fits beingsuch as to permit this, which contributes materially to the ease of eldassembly. l

The outer tube is grounded at frequent intervals and its outer surfaceis bare. It can .be supported in any convenient manner and since it isat ground potential no .costly insulators are required. Any conventionalform of pipe clamp may be used. The copper tubing because of its size,is quite heavy and it is found convenient .to use it in lengths of 12-15feet. The joints may be staggered between the inner and outer metaltubes or they can be made at the same place with no difficulty as shown.Joints in the insulation tube are preferably simple overlaps formed bycounterboring the end of one and reducing the outside `diameter oftheother until they can be telescoped with' suicient friction to retainthem in position as shown at 43 in Figure 5.

In Figure l at 44 is shown a clamp performing the dual function ofmechanically and electrically securing together the substantiallyabutting ends of two sections of the outer tube and of providing asupport for the same from any structural element available. The clampcomprises two substantially semi-circular parts provided with vthe upperflanges 46 perforated to receive clamp bolts 4l and the lower perforatedflanges 48 likewise provided with bolts and extending downwardly andslotted at 40 to be slidably supported on a pin 50 spanning the ears 5lon the A55 and a T-clamp at 56. For reducing the diameter of the bus forextensions carrying lighter loads resort may be had to a suitablepressor sweat-fitted reducer coupling 57.

Electrical connections to the outer pipe or tube are made by means of asimple strap clamp 58 made of suitably heavy copper to carry therequired current. Clamping bolts are passed through the ears 59 thereonand a lug B0 is provided with four openings to receive bolts forattaching terminal lugs on Welder cables. Obviously the connector strapsmay be applied anywhere that it is convenient on any unoccupied space onthe surface of the bus. It will be noticed that `all outside fittingsengage the outer surface only of the bus sections and have no portionsextending within the cylinder dei-ined by the outer surface `of theouter tube. v

The inner tube 4I has its sections joined together by appropriatefittings whose outer surfaces engage .the inner surfaces of the tubesections and no part of `which extends beyond the outer surface of theinner tubes, except in a few special cases. For a simple butt jointthere is shown at El a longitudinally perforated nipple having thecircumferential flange 62 of an overall diameter the same as the outsidediameter of the inner tube. The tube ends are fitted over the nipple andabut the flange. It has been found that current conductivity is best ifa shrink-fit cornbined withsolder sweating is used at these innerjoints. It is obvious that 45 and 90 elbows such as shown at 63 and 64may be readily provided, the flange being extended to :till out thespace between the ends of the straight tube sections. At such elbows itis convenient to taper off the ends .of `the insulation tubes and tojoin them and cover the enlarged portion of the inner fitting withsuitable cambric tape insulated with a proper impregnant as iscustomary. This can be done before applyingthe outer tube sections andtheir clamp parts.

One of the important features of the present invention is the ease withwhich taps can be taken from the tubular conductors. The outer tap hasalready been described and reference should be had to the vdrawing forthe manner of effecting a tap to the inner tube. Each inner tube isprovided, `wherever a tap may be required, with a rectangular slot 11 asseen in Figures 2 and 3, the long axis extending longitudinally of thetube. The insulation tube and the outer tube arevdrilled with circularapertures 18 having a diameter subthe rectangular slot in the innermetal tube.

The actual connecting member isa T-headed copper bolt having acylindrical shank 19 and the head 8l! curved on its undersurface to thesame radius as the inner wall of the inner tube. This head may be passedthrough the openings in the outer and insulation tubes, and, by proper'orientation, through the slot in the inner tube which is sloped andsized like the head. It may then be rotated 90 about the axis of theshank to the position shown in Figures 2 and 3 whereby the curvedundersurface of the head beyond the shank will closely t and contactwith the inner wall of the inner tube. Next a copper sleeve 8l, bestshown in Figure 4, is slid over the shank of the bolt. This sleeve hasits lower edge 82 curved to t the outer surface of the inner tube 4l asshown in Figure 4. Extending from this edge are the two lugs 83 eachhaving a transverse width the same as that of the narrow dimension ofthe slot 'I1 and a length at least that of the wall thickness of tube4l. These projections extend down beside the head 80 as seen in Figure5, and fit into the slot, closely engaging the walls thereof to preventrotation of the sleeve in the tube and also to prevent rotation of theT-headed bolt.

With the bolt and sleeve in position they are covered by, an insulationtube 85, the lower end of which is curved to t the outer surface of theinner conducting tube. The outside diameter of this insulation is suchas to closely nt through the openings in the main insulation tube andthe outer conducting tube. Over this tube 85 is closely fitted theopening of a shield 86 whose inner surface is curved to iit the outersurface of the outer tube. To retain this shield in position a secondinsulation sleeve 81 closely fits over the tube 85 and has its lower endarranged to bear on the shield and hold it in position. The upper endsof the copper sleeve 8l and the insulation tubes 85 and 81 are cut offat right angles and in alignment, and bearing on their outer ends is themetal washer 88 held in position by the lock nut 89 which pressesdownwardly on the copper sleeve 8| and draws upwardly on the shank ofthe bolt to which it is threaded and tightly clamps the inner conductortube between the lower end of the sleeve and the upper face of the bolthead,A

providing `excellent electrical contact.

Current is taken off from the bolt by attaching thereto a bus plate 90by means of a second nut 9|. This plate may be conveniently perforatedwith two holes on each side of the bolt to receive small bolts forclamping the terminal lugs oi welding cables thereto.

Preferably the inner terminals or taps, just described, are spaced closeto the outer tube 'terminal straps as shown at the right in Figure l andwhere a number of welding devices are used in production work whichrequires frequent changes in their positions, it is convenient to applyterminals at say six foot intervals. It may sometimes be desirable toprovide for future needs by providing the apertures for inner terminalsand covering these with suitable insulation so that the positions areavailable for inserting the terminals when required.

Having thus described the invention, what is vstantially equivalent tothe maximum length of l lili [il l aligned openings in the outerconductor and inclaimed as new and desired to be secured by LettersPatent is:

1. A bus system comprising a section of co-axially arranged inner andouter tubular conductors insulated from each other and a line tap forthe inner conductor including a Theaded bolt, a metal sleeve slidablyfitting the shank thereof, the inner tube having a longitudinallydisposed opening to just pass said bolt head, the outer tube having acircular opening just larger than the major Vaxis of said head, the headbeing positioned transversely o and within the inner tube with thesleeve surrounding the bolt shank and bearing on the outer surface ofthe inner tube, an insulating sleeve surrounding the metal sleeve andhaving its inner end bearing on the inner tube, and a washer and locknut on the bolt to clamp the inner tube between said head and metalsleeve. n

2. The bus system as dened in claim 1 in which the undersuriace of thehead and the lower end of the metal sleeve are curved to closely fit theinner and outer surfaces respectively of the inner tube.

3. The bus system as defined in claim 1 in which the metal sleeve hasits lower end provided with spaced lugs tting beside said head and-closely within said opening to prevent rotation of the said bolt.

4, The bus system as defined in claim l in which the undersurface of thehead and the lower end of the metal sleeve are curved to closely fit theinner and outer surfaces respectively of the inner tube, said sleevehaving extensions thereon lying alongside of said bolt head and fittingin said inner tube opening to prevent rotation of said bolt afterinitial positioning.

5. A bus system for delivering power to a welder, comprising a sectionof coaxially arranged inner and outer one"piece, substantially closedtubular conductors insulated from each other, and a line tap positivelyclamped to the inner and outer surfaces of a wall of the inner of saidtubular conductors for connection to the welder, said tap passingthrough an aperture provided in the wall oi the outer conductor for thepurpose and insulated therefrom, said tap being spaced from andindependent of the ends of the section.

6. A bus system comprising coaxially arranged one piece inner and outersubstantially closed tubular conductors insulated from each other by atube of insulation, the inner conductor having an opening through thewall of less area than aligned openings in the outer conductor and inesulation tube, a tap comprising relatively movable clamp elements bothadapted to pass through the larger openings and one through the smalleropening, and means to urge said clamp elements toward each other toengage the wall of the inner tube for mechanical and electricalconnection thereto.

7. A bus system comprising coaxially arranged one piece inner and outersubstantially closed tubular conductors insulated from each other by atube of insulation, the inner conductor having an opening through thewall of less area than sulationl tube, a tap comprising relativelymovable clamp elements both adapted to pass through the larger openingsand one through the smaller opening, means to urge said clamp elementstoward each other to engage the wall of the inner tube for mechanicaland electrical connection thereto, and means to insulate said clampelements from the outer conductor.

8. A bus system comprising coaxially arranged one piece inner and outersubstantially closed tubular conductors insulated from each other by a`tube of insulation, the inner conductor having an opening through thewall of less area than aligned openings in the outer conductor andinsulation tube, a tap comprising relatively slidable telescoped clampelements having heads both adapted to pass through the larger openingsand one through the smaller opening, and means on one of said clampelements and engaging the other to urge the heads toward each other toengage the inner tube for mechanical and electrical connection thereto.

9. A bus system for delivering power to a Welder, comprising a sectionof coaxially arranged inner and outer substantially closed tubularconductors spaced fron each other, continuous tubular insulating meansin the space between the conductors, and a line tap clamped to the innerand outer surfaces of a Wall of a continuous por-

